In previously funded research (National Institute of Aging, 1999-2005), we used theories of two-choice decision making to explore the effects of aging on cognition. The theories were severely challenged by wide ranges of performance levels and the competing demands of large numbers of experimental conditions, but they were successful in jointly accounting for all the response time and accuracy data for young and older adults. The theories allowed separation of the components of processing involved in two-choice decisions and determination of which components were affected by aging. The quality of the information obtained from stimuli was usually not worse for 60-90 year old adults than college students, although the older adults were generally slower in non-decision components of processing and they adopted more conservative decision criteria. In the proposed research, the theories will be applied to four main issues, all central to the mission of NIA: First, we plan to investigate whether performance on simple two-choice tasks can be improved for older adults by training on laboratory tasks and/or computer-based training packages, which components of processing identified by the theories can be improved with training, and under what conditions do improvements in processing transfer from one task to another? Second, we plan to investigate which components of processing are affected for patients with early Alzheimer's disease and patients with Mild Cognitive Impairment compared to normal healthy adults. If one or another of the components is differentially affected among the three populations, it might provide a signature to aid in diagnosis. Third, we plan to examine the effects of aging on a broad sample of healthy young and older adults. Most of our completed work has focused on adults with college educations. We may find that aging leads to larger decrements in performance and components of processing for adults with less education and/or lower cognitive abilities. Fourth, we plan to extend our theories and empirical investigations to tasks that require associative memory, a kind of memory that often shows large decrements with aging. In addition to these four main issues, we plan to check that conclusions about the effects of aging, impairment, practice, and task requirements are consistent across theories of two-choice decision making, and to check the conclusions from the standard two-choice response time paradigm against conclusions from the response signal paradigm.